1. Field of the Invention
The invention relates to a spring strut, which comprises a pneumatic spring and an oscillation damper and is fitted between a vehicle body and a vehicle wheel. The pneumatic spring has a spring chamber delimited by a rolling bellows which is connected to a receptacle and to a container or to a rolling contact piston fixed to a container.
2. Description of the Related Art
Wheel-guiding forces are exerted on the spring strut by steered wheels via an axle stub, for example. The forces perpendicular to the axis of the oscillation damper, in particular, are problematic since these produce bending moments on the oscillation damper and hence on the piston rod, the end of which is connected in a moveable manner to the vehicle body. The bowing of the piston rod can lead to jamming in the piston-rod guide, resulting not only in high frictional and clamping forces but also high transverse bearing forces on the fixing point of the piston rod on the vehicle body.
To reduce the bending forces acting on the piston rod and hence to reduce the transverse bearing forces on the fixing point of the piston rod on the vehicle body in the case of spring struts with pneumatic springing, DE-A 2 063 448 and DE-A 2 100 338 disclose arranging the axis of the pneumatic spring obliquely to the axis of the oscillation damper. The disadvantage is the asymmetric deformation of the rolling bellows of the pneumatic spring that occurs in the case of obliquely positioned pneumatic springs, leading to wear and hence to a shorter life for the rolling bellows. One possibility for reducing the deformation work of the rolling bellows, a possibility that is associated with a high outlay in terms of production and assembly and is therefore very expensive, is indicated in DE-A 2 100 338, the container of the oscillation damper being connected to a three-dimensionally curved rolling-contact body that is complicated to produce.
It is the object of the present invention to create a spring strut that is provided with a pneumatic spring and can be produced economically, which, while being of simple construction, effects a reduction or compensation of the transverse bearing forces caused by the wheel-guiding forces and hence also of the bending forces acting on the piston rod and, at the same time, exhibits as little as possible stress on the rolling bellows.
According to the invention, this object is achieved with the distinguishing features of claim 1. Advantageous refinements and further embodiments are the subject matter of the subclaims.
According to the invention, a spring strut that is of simple construction and can be produced economically is created by providing a body that is acted upon on one side by the pressure in the spring chamber and is in operative connection with the oscillation damper. This body has an effective area that extends obliquely to the axis of the oscillation damper and exerts a transverse force that is dependent on the pressure in the spring chamber and is perpendicular to the axis, thereby ensuring in a simple manner a reduction or compensation of the forces exerted by the wheel-guiding forces. The transverse force that can be achieved is dependent on the pressure in the spring chamber, and the obliquity and effective size of the effective area, allowing adaptation to the required reduction in the forces occurring at the fixing point of the piston rod in the vehicle body by changing the obliquity of the effective area.
Minimization of the stress on the rolling bellows is achieved if, according to a further feature of the invention, the axis of the pneumatic spring coincides with the axis of the oscillation damper. Over the entire spring travel, the rolling bellows moves without asymmetric deformation in an annular space which is delimited, on the one hand, by the rolling-contact piston and, on the other hand, by a protective tube, the axis of the protective tube lying on the axis of the rolling-contact tube. The rolling bellows has a simple shape since it is secured on a cylindrical portion of the body and this body is arranged in a sealing and axially displaceable manner on the piston rod and has an effective area formed by the end of the body and extending obliquely to the axis.
A simple overall structure of the spring strut is obtained if the end of the body has an outer extension and hence acts on a flexible mounting component arranged on the end of the piston rod. It is also advantageous if the body forms a contact surface for a flexible compression stop of the oscillation damper.
To ensure that the rolling bellows, which is secured by one end on the rolling-contact piston connected to the container of the oscillation damper and by the other end on the cylindrical portion of the body, is not subjected to torsion, the outer extension of the body has a supporting surface that extends perpendicular to the axis of the oscillation damper and is arranged so as to interact with a corresponding mating surface of the mounting component. For particular ease of motion, a pivot bearing is arranged between the supporting surface of the outer extension and the mating surface of the mounting component, this pivot bearing advantageously being designed as a rolling-contact bearing.
In another embodiment, the body that has the effective area extending obliquely to the axis is fitted between the outer wall of the container and the inner wall of the rolling-contact piston and sealed off from the outside. The force exerted on the body by the pressure in the spring chamber acts on the container and counteracts the effective wheel-guiding forces in accordance with the position of installation of the body. There are different ways of producing this effective area extending obliquely to the axis and securing it in such a way as to form a seal with respect to the outside. For example, the rolling-contact piston can be designed in such a way that it has this effective area, i.e. is in one piece with this effective area.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.